As one of prevalent PDLs, PostScript (which is a registered trademark of Adobe Systems Corporation, U.S., and will be abbreviated as “PS” hereinafter) is known. PS Levels 1 and 2 are older versions, and PS Level 3 is introduced as the current version. With PS Levels 1 and 2, three different color spaces RGB, CMYK, and Gray are selectable, and one of these color spaces used is obtained by interpreting a description in print data.
Therefore, a printer determines which of DeviceRGB, DeviceCMYK, and DeviceGray is used, converts input signals into C (Cyan), M (Magenta), Y (Yellow), and K (Black) on a printer color space by a simple process according to the determination result, and then executes a print process, as shown in FIG. 1. For example, in the case of DeviceRGB, i.e., RGB signals (Red, Green, and Blue), an inverse unit (101) inverses the RGB signals into CMY signals, which undergo an Under-Color Removal (UCR) process and Black Generation (BG) process in a UCR & BG unit (102), thus generating CMYK signals. In case of DeviceCMYK, i.e., CMYK signals, since this color space is the same as the output printer space, the CMYK signals are directly output without any process. Furthermore, in the case of DeviceGray, i.e., one Gray color, since the luminance and density are inverted, the Gray signal is inverted by an inverse unit (103) to generate a K component, i.e., CMYK signals including only the K component, thus making a print process.
On the other hand, PS Level 3 allows one to apply a color management process to DeviceRGB, DeviceCMYK, or DeviceGray upon outputting by designating a UseCIEColor parameter. That is, if the UseCIEColor parameter is “true”, a color processing flow shown in FIG. 2 is applied; if it is “false”, the process shown in FIG. 1 is applied.
The color management process shown in FIG. 2 will be described below. In the case of DeviceRGB, an RGB Source Profile, which is set in advance, is selected, and DeviceRGB is converted into an XYZ color space (204), which is normalized to specify colors, using the selected profile. The XYZ color space is converted into CMYK values in accordance with an Output Profile (205) as a profile which stores information about an appropriate combination of CMYK values to output that XYZ color space. In this way, the printer outputs input RGB signals to have correct values in terms of chromaticity.
DeviceCMYK inputs are converted into the XYZ color space (204) using a CMYK Simulation Profile (202), which is set in advance. Also, DeviceGray inputs are converted into the XYZ color space (204) using a Gray Profile (203) which is pre-stored in a device. Since the conversion process from the converted XYZ color space (204) into CMYK values is the same as that for DeviceRGB, description thereof will be omitted.
Actual flows of respective signals will be explained below using FIG. 8. When the UseCIEColor parameter=true, DeviceRGB is converted into CIEBasedABC or CIEBasedDEF, DeviceCMYK is converted into CIEBasedDEFG, and DeviceGray is converted into CIEBasedA. Also, these color spaces are converted into the XYZ color space as the intermediate color space of PS color management. Next, the XYZ color space is converted into CMYK values according to setups of the Output Profile (205).
As can be seen from FIG. 8, a larger number of conversion processes than in the process shown in FIG. 1 for PS Level 1 or 2 are required, and a longer calculation time is required. Especially, in the case of an image with a large bitmap, individual pixels must undergo such conversion processes, thus taking more time.
Color management of PS Level 3 shown in FIG. 2 is not switched for respective objects which are categorized to Text, Graphics, Image, and the like, and black, e.g., R=G=B=N %, C=Y=M=N %, or K=N % (N=0% to 100%), is normally converted into process black as a combination of four colors C, M, Y, and K, which represent a chromaticity value optimal to a printer by color management.
As described above, the UseCIEColor parameter is normally set “true”. Upon outputting even an image that appears to be a monochrome image on the screen, to a color printer, it is reproduced using process black as a combination of four color components C, M, Y, and K by color management, i.e., such image is normally output as a color image.
Therefore, an image, graphics, and text, which are created or input by the user as monochrome ones on the screen of a host computer, are output as a color image, graphics, and text. Graphic Arts users who preferably use PS and place importance on color tincture in color management are rarely dissatisfied with the outputs being color outputs, and no problem is posed.
However, due to the spread of PS to offices in recent years, office users who create and print documents that mainly include text do not prefer the complicated, time-consuming color management process described above using FIG. 8, since they normally create monochrome documents and require a higher print speed rather than high color reproducibility. Also, only one UseCIEColor parameter is set for all of DeviceRGB, DeviceCMYK, and DeviceGray, and cannot be individually set.
PS Level 3 can define a Separation color space and DeviceN color space to cope with an expensive dedicated printing machine which prints using special color agents, in addition to the above CMYK, RGB, and GRAY color spaces. For example, the user of a dedicated printing machine (e.g., an image setter or the like) uses the Separation color space to cope with colors which cannot be reproduced by basic CMYK, and the DeviceN color space to broaden the gamut by adding colors to standard CMYK colors.
The Separation color space and DeviceN color space are mainly used in print processes by the dedicated printing machine, which entails a very high print cost. Therefore, test print processes are often made using a normal color printer using four colors C, M, Y, and K.
As a problem posed in such case, the Separation color space and DeviceN color space are those for the dedicated printing machine with advanced functions, and cannot be directly reflected on the color space of a normal color printer that uses CMYK color agents. That is, the normal color printer cannot directly print data of the Separation color space and DeviceN color space.
Hence, PS Level 3 allows a normal color printer to print data of the Separation color space and DeviceN color space by describing a substitute color space.
For example, the Separation color space is defined as follows:
[ /Separation(LogoGreen)/DeviceCMYK{ dup 0.84 mulexch 0.0 exch dup 0.44 mulexch 0.21 mul}] setcolorspace
This description means that print data represents color “LogoGreen”, and its color space corresponds to a space color obtained by converting parameters described in the curled brackets { . . . } if it is expressed by the CMYK color space (substitute color space).
Therefore, when the above print PS data is input, the color space of color “LogoGreen” is expressed by parameters of a given CMYK color space, and the values of color “LogoGreen” described in print data to be subsequently received are processed to indicate CMYK values on the substitute color space.
A description in case of the DeviceN color space is as follows:
[ /Indexed[ /DeviceN[/Cyan /Black]/DeviceCMYK{0 0 3 −1 roll}]255<6605 6806 6907 6B09 6C0A ...>] setcolorspace
This description means that a print process is made using two color agents (cyan and black) (an example of N=2 of DeviceN), and defines conversion into a substitute color space using parameters defined in the subsequent curled brackets { . . . } when a color space expressed by these two colors is expressed by the substitute color space CMYK.
As described above, PS Level 3 allows a normal CMYK printer to print by defining the Separation color space or DeviceN color space using the substitute color space.
In the case of the above example of the Separation color space, since the substitute color space CMYK is used, the subsequent processing is performed under the assumption that data on the “CMYK” color space shown in FIG. 2 are input. The same applies to the example of the DeviceN color space (when the UseCIEColor parameter=True).
Upon reception of data of the Separation color space or DeviceN color space, many color space conversions, i.e., conversion into the substitute color space, conversion of that substitute color space into the standard color space XYZ, and conversion of the color space XYZ into CMYK values based on an Output Profile of a printer, are required. Therefore, when an object to be printed is a bitmap image, since individual pixels must undergo these conversion processes, the time required for these processes is not negligible, resulting in a drop in the print throughput.